The overall goal of the present proposal is to determine the molecular/cellular mechanism(s) involved in the maturation process of cumulus oocyte complexes (COCs). Proper maturation of the COC is critical to reproductive success in vivo and in vitro. Our lack of a complete understanding of this maturation process restricts our ability to manage fertility in vivo and hinders implementation of ART such as in vitro fertilization and in vitro maturation. Recent studies by our laboratory and others have begun to shed light on a small family of nuclear transcription factors, RUNX1 and RUNX2, as key transcriptional regulators involved in COC expansion. Our preliminary data demonstrated that Runx1 and Runx2 expression is highly induced in cumulus cells of periovulatory follicles. We also found that RUNX1 and RUNX2 regulate the expression of Ptgs2 (a rate-limiting enzyme in the biosynthesis of prostaglandins) and Hapln1 (a stabilizer of cumulus matrix) in mural granulosa cells and/or cumulus cells. Both gene products are known to play crucial roles in COC expansion. Most importantly, our pilot study demonstrated that over-expression of dominant negative RUNX in cumulus cells blocked COC expansion. Based on these novel findings, we hypothesized that RUNX1/2 are essential transcriptional regulators necessary for the gonadotropin surge-induced COC expansion. This hypothesis will be tested by first demonstrating the functional significance of Runx1/2 expression in cumulus cells (Aim #1). Secondly, we will determine the regulation action(s) of RUNX1 and RUNX2 on their target genes (Aim #2). Next, we will determine the regulatory mechanism(s) of Runx1 and Runx2 expression in cumulus cells (Aim #3). These 3 Aims will be studied using rat COCs. To insure that the data obtained from rat studies is translatable to humans, RUNX1/2 and their target gene expression profile will be also verified using human cumulus cells collected throughout the periovulatory period. We will also examine the correlation of the cumulus expression of RUNX1/2 and their target genes to oocyte quality, fertilization, and embryo development using COCs obtained from women undergoing IVF (Aim #4). These human studies will serve as a foundation for future translational/clinical application. The information obtained from the proposed studies will not only advance our understanding of the mechanism involved in COC maturation, but also be instrumental for future translational/clinical application(s), thus leading to improved management of fertility in vivo and in vitro.